Aerial treatment of the migratory locust, Locusta migratoria (L.) (Orthoptera: Acrididae) with Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) in Australia

Between November 1998 and March 1999, bands of nymphs of Locusta migratoria were aerially treated using a ULV oil formulation of strain FI-985 of Metarhizium anisopliae var. acridum. At a dose of 3–4×10¹² conidia/ha, there was <10% survival of locusts in treated sorghum crops, open grassland or open woodland with grass. Decline was less at lower doses or in dense woodland. During the first week after treatment, bands showed little change in numbers, but then rapidly declined in size and rate of movement. The decline was slower where vegetation was tall or dense, or where bands were large and moved out of the treated area a few days after spraying. In areas where bands were treated with Metarhizium, populations were suppressed in that few adult swarms formed. Adjacent untreated areas had many adult swarms which had to be controlled using chemical insecticides. Preventive locust control, as currently practised in Australia, involves beginning treatment when areas of band and swarm are small and the potential for direct damage limited. The clear demonstration that Metarhizium can suppress small local populations of L. migratoria indicate that it could be a valuable component of preventive control programmes against this species. The delay in mortality when treating with Metarhizium would be no impediment to its use in such programmes.